System and method of pivoted stent deployment

ABSTRACT

The invention provides a stent-graft system comprising a graft member and a stent having a connection end interconnected with the graft member and a free end opposed thereto. A belt retaining structure is provided at the stent free end. A belt is releasably retained in the belt retaining structure and is configured to constrain the stent free end independent of the stent connection end. A method of securing at least one end of a stent-graft within a vessel is also provided.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/861,716, titled “System and Method of Pivoted Stent Deployment”,filed Sep. 26, 2007, by Isaac J. Zacharias et al., which is incorporatedby reference herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a system for the treatment of disordersof the vasculature. More specifically, the invention relates to a systemfor the treatment of disease or injury that potentially compromises theintegrity of a flow conduit in the body. For example, an embodiment ofthe invention is useful in treating indications in the digestive andreproductive systems as well as indications in the cardiovascularsystem, including thoracic and abdominal aortic aneurysms, arterialdissections (such as those caused by traumatic injury), etc.

For indications such as abdominal aortic aneurysms, traditional opensurgery is still the conventional and most widely-utilized treatmentwhen the aneurysm's size has grown to the point that the risk ofaneurysm rupture outweighs the drawbacks of surgery. Surgical repairinvolves replacement of the section of the vessel where the aneurysm hasformed with a graft. An example of a surgical procedure is described byCooley in Surgical Treatment of Aortic Aneurysms, 1986 (W. B. SaundersCompany).

Despite its advantages, however, open surgery is fraught with highmorbidity and mortality rates, primarily because of the invasive andcomplex nature of the procedure. Complications associated with surgeryinclude, for example, the possibility of aneurysm rupture, loss offunction related to extended periods of restricted blood flow to theextremities, blood loss, myocardial infarction, congestive heartfailure, arrhythmia, and complications associated with the use ofgeneral anesthesia and mechanical ventilation systems. In addition, thetypical patient in need of aneurysm repair is older and in poor health,facts that significantly increase the likelihood of complications.

Due to the risks and complexities of surgical intervention, variousattempts have been made to develop alternative methods for treating suchdisorders. One such method that has enjoyed some degree of success isthe catheter-based delivery of a stent-graft via the femoral arteries toexclude the aneurysm from within the aorta. Illustrative stent-graftsand methods of delivery thereof are described in U.S. Patent ApplicationPublication Nos. 2003/0125797A1, 2004/0138734A1 and U.S. Pat. No.6,295,019, each of which is incorporated herein in its entirety byreference herein.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a stent-graft system comprising agraft member and a stent having a connection end interconnected with thegraft member and a free end opposed thereto. A belt retaining structureis provided at the stent free end. A belt is releasably retained in thebelt retaining structure and is configured to constrain the stent freeend independent of the stent connection end.

In another aspect, the invention provides a method of securing at leastone end of a graft within a vessel. The method comprises: positioningwithin the vessel a stent-graft comprising a stent and a graft with aconnection end of the stent connected to an end of the graft, the stenthaving a free end opposite the connection end, the stent free endincluding a belt retaining structure with a belt releasably retainedthereabout; deploying the stent connection end within the vessel;repositioning the stent-graft within the vessel; and releasing the beltto deploy the free end of the stent.

Other aspects and advantages of the present invention will be apparentfrom the detailed description of the invention provided hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIG. 1 shows a portion of an endovascular graft according to anembodiment of the present invention in a contracted state for deliverythrough a catheter.

FIG. 2 shows a flat pattern of an embodiment of a stent in accordancewith the present invention.

FIG. 3 shows a flat pattern of an alternative embodiment of a stent inaccordance with the present invention.

FIG. 4 shows a flat pattern of another alternative embodiment of a stentin accordance with the present invention.

FIG. 5 shows a portion of an endovascular graft according to anembodiment of the present invention partially deployed within theinternal vasculature of the patient.

FIG. 6 shows the endovascular graft portion of FIG. 5 fully deployedwithin the internal vasculature of the patient.

FIG. 7 shows a portion of an endovascular graft according to anembodiment of the present invention partially deployed within an aorticarch of the patient.

FIG. 8 is an isometric view of a pivot fitting in accordance withanother embodiment of the present invention.

FIG. 9 is an end view of the pivot fitting of FIG. 8.

FIG. 10 is a cross-sectional view along the line 10-10 in FIG. 9.

FIG. 11 is a cross-sectional view similar to FIG. 10 illustratingschematically a stent thereon in a contracted state.

FIG. 12 is a cross-sectional view similar to FIG. 10 illustratingschematically a stent thereon in a partially deployed state.

FIG. 13 is a perspective view illustrating a stent in the partiallydeployed state of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

Referring to FIG. 1, a portion of an illustrative endovascular graft 10is shown in its contracted configuration. Unless otherwise stated, theterm “graft” or “endovascular graft” is used herein to refer to aprosthesis capable of repairing and/or replacing diseased vessels orportions thereof, including generally tubular and bifurcated devices andany components attached or integral thereto. For purposes ofillustration, the graft embodiments described herein may be used in theendovascular treatment of abdominal aortic aneurysms (AAA) or thoracicaortic aneurysms, however, other applications are within the scope ofthe present invention. For the purposes of this application, withreference to endovascular graft devices, the term “proximal” describesthe end of the graft that will be oriented towards the oncoming flow ofbodily fluid, typically blood, when the device is deployed within a bodypassageway. The term “distal” therefore describes the graft end oppositethe proximal end. Finally, while the drawings in the various figures areaccurate representations of the various embodiments of the presentinvention, the proportions of the various components thereof are notnecessarily shown to exact scale within and among or between any givenfigure(s).

An end of the graft 10 is illustrated and may represent the proximal ordistal end of the graft 10. The graft 10 includes a generally tubularstructure or graft body section 13 comprised of one or more layers offusible material, such as expanded polytetrafluoroethylene (ePTFE). Aninflatable cuff 16 is disposed at or near the end 14 of graft bodysection 13. A neck portion 23 is disposed in the vicinity of graft bodysection end 14 and serves as an additional means to help seal thedeployed graft against the inside of a body passageway. Graft bodysection 13 forms a longitudinal lumen 22 configured to confine a flow offluid therethrough.

A attachment ring 24 is affixed to or integrally formed in graft bodysection 13, or as shown in FIG. 1, at or near graft body section end 14and neck portion 23. In the embodiment of FIG. 1, attachment ring 24 isa serpentine ring structure comprising apices 28. Other embodiments ofattachment ring 24 may take different configurations. Attachment ring 24may be made from any suitable material that permits expansion from aconstrained state, most usefully a shape memory alloy havingsuperelastic properties such as nickel titanium (NiTi). Other suitableattachment ring 24 materials include stainless steel, nickel-cobaltalloys such as MP35N, tantalum and its alloys, polymeric materials,composites, and the like. Attachment ring 24 (as well as all stents andattachment rings described herein) may be configured to self-expand fromthe illustrated radially constrained state.

Some apices 28 may also comprise a attachment ring connector element 30(see FIGS. 5 and 6). The number of connector elements 30 may vary andcan be distributed, for example, on every apex, every third or fourthapex, or any other pattern are within the scope of the presentinvention.

Graft 10 further comprises one or more stents 40 having, in the deployedstate (see FIG. 6), a generally free end 42 and a connection end 44.FIGS. 1 and 5-6 illustrate a proximal stent 40, but the stents 40 mayadditionally or alternatively be provided on the distal end of the graft10. In the case of a bifurcated graft, a stent 40 may be provided on thedistal end of each leg of the bifurcated graft.

As shown in FIGS. 1 and 5-6, stent 40 is typically, though notnecessarily, made a part of graft 10 by having the connection end 44affixed or connected to attachment ring 24 via connector elements asdescribed in detail below. The connection end 44 of stent 40 may also beaffixed or embedded directly to or in neck portion 23 and/or otherportions of graft body section 13. In addition, the attachment ring andthe stent may not be mechanically or otherwise fastened to one anotherbut rather unified, formed of a monolithic piece of material, such asNiTi.

This configuration of stent 40, attachment ring 24, neck portion 23, andcuff 16 helps to separate the sealing function of cuff 16, whichrequires conformation and apposition to the vessel wall within whichgraft 10 is deployed without excessive radial force, from the anchoringfunction of stent 40 (attachment ring 24 and neck portion 23 playintermediate roles). As will be described in more detail hereinafter,the stents 40 of the present invention permit improved positioning ofthe graft 10 prior to stent anchoring, thereby facilitating betterplacement and sealing of the graft 10.

Referring to FIGS. 2-4, each stent 40 of the present invention generallycomprises a series of interconnected struts 41. As illustrated, thestruts 41 can have various configurations and lengths. Each stent 40further comprises stent connector elements 48 at the connection end 44thereof. The stent connector elements 48 are configured to be affixed orotherwise connected to attachment ring connector elements 30 viacoupling members (not shown), for example, threads or wires. The stents40 may be manufactured from any suitable material, including thematerials suitable for attachment ring 24. When manufactured from ashape memory alloy having superelastic properties such as NiTi, thestents 40 may be configured to self-expand upon release from thecontracted state. The strut structure is often formed as a flatstructure, as illustrated in FIGS. 2-4, and thereafter, wrapped andconnected in a cylindrical or other configuration, as illustrated inFIG. 1.

Each stent 40 includes one or more barbs 43. A barb 43 can be anyoutwardly directed protuberance, typically terminating in a sharp pointthat is capable of at least partially penetrating a body passageway inwhich graft 10 is deployed (typically the initial and medial layers of ablood vessel such as the abdominal aorta). The number of barbs, thelength of each barb, each barb angle, and the barb orientation may varyfrom barb to barb within a single stent 40 or between multiple stents 40within a single graft. Although the various barbs 43 (and tuck pads 45discussed below) may be attached to or fixed on the stent struts 41, itis preferred that they be integrally formed as part of the stent struts41, as shown in the various figures.

When stent 40 is deployed in the abdominal aorta, for example, typicallyin a location proximal to the aneurysm and any diseased tissue, barbs 43are designed to work in conjunction with the distally-oriented bloodflow field in this location to penetrate tissue and prevent axialmigration of graft 10. As such, the barbs 43 in the FIG. 1 embodimentare oriented distally with respect to graft body section 13. However,the number, dimensions, configuration and orientation of barbs 43 mayvary significantly, yet be within the scope of the present invention.

Struts 41 may also comprise optional integral tuck pads 45 disposedopposite each barb 43. During preparation of graft 10 (and therefore thestents 40) into its reduced diameter delivery configuration, each barb43 is placed behind a corresponding strut 41 and/or optional tuck pad45, if present, to thereby prevent the barbs 43 from contacting theinside of a delivery sheath or catheter during delivery of the deviceand from undesired contact with the inside of a vessel wall. Asdescribed in U.S. Pat. No. 6,761,733 to Chobotov et al., the completedisclosure of which is incorporated herein by reference, an initialstage release belt 35 disposed about the struts 41 retain the stent 40in this delivery configuration. The initial stage release belts 35retain the contracted stent 40 on a guidewire chassis 12 or the like.

The number of initial stage belts 35 varies in accordance with thestructure of the stent 40. For example, the stents 40 as illustrated inFIGS. 2 and 4 have proximal and distal segments and two correspondinginitial stage belts 35, one about the proximal segment and one about thedistal segment, are used to secure the stent 40 as shown in FIG. 1. Inshorter stents 40 having a single segment, like the stent 40 illustratedin FIG. 3, a single initial stage belt 35 is typically used to securethe stent 40. Upon deployment of the stent 40, by releasing the initialstage belt(s) 35, the radial expansion of stent 40 results in adisplacement of struts 41 so that the distance between them increases.As the struts 41 separate, the barbs 43 are freed from behind the struts41 and optional tuck pads 45, if present, and engage the wall of thevessel being treated. To enhance the engagement of the barbs 43 in thevessel wall 20, the barbs 43 may be designed to work in conjunction withthe distally-oriented blood flow field, that is, the barbs 43 areoriented distally, however, they do not have to be. In the illustrativeembodiment, the barbs 43 at the proximal end are oriented distally,while the barbs 43 at the distal end are oriented proximally.

While secure engagement of the barbs 43 in the vessel wall 20 isdesirable to prevent axial migration of graft 10, such engagement isgenerally permanent and not subject to modification. Attempts toreposition the stent 40 or graft 10 after engagement of the barbs 43 inthe vessel wall 20 may cause tearing or other damage to the vessel wall20.

Referring to FIGS. 2-4, each stent 40 of the present invention includesa belt retaining structure 50 provided along the crowns 47 at the freeend 42 of the stent 40. In the embodiments illustrated in FIGS. 2 and 3,the belt retaining structure 50 includes a plurality of mushroom shapedconnectors 52 extending from the crowns 47. The mushroom shapedconnectors 52 may be provided at each crown 47, as illustrated, or inany configuration with respect to the crowns 47. Referring to FIGS. 1and 5, a releasable secondary stage belt 53 is positionable about themushroom shaped connectors 52 to retain the stent free end 42 in acontracted state until the secondary stage belt 53 is released, forexample, via a release wire 55. In the embodiment illustrated in FIG. 4,the belt retaining structure 50 includes a through hole 54 provided in aplurality of the crowns 47. A releasable belt (not shown) is threadedthrough the through holes 54 and pulled tight to retain the stent freeend 42 in a contracted state until the belt is released. Other beltretaining structures 50 along the stent free end 42 may also beutilized.

As shown in FIG. 5, upon release of the initial stage belts 35, thestent connection end 44, the attachment ring 24, and the graft 10 expandwhile the secondary stage belt 53 engages the belt retaining structure50 and retains the stent free end 42 in the generally contractedcondition. The stent connection end 44 and the graft 10 expand based onthe self expanding nature of the stent 40 and also the force of thedistal fluid flow into the graft 10. The struts 41 and barbs 43 areconfigured such that when the belt retaining structure 50 is in placeand the stent free end 42 is restrained, the barbs 43 do not extendsufficiently radially to engage the vessel wall 20, but instead remainspaced therefrom. As such, the graft 10 and stent 40 may be moved andrepositioned without the barbs 43 engaging and damaging the vessel wall20. In at least one embodiment of the invention, the barbs 43 areaxially positioned closer to the stent free end 42 than the stentconnection end 44 to further ensure the barbs 43 will not contact thevessel wall 20 in the partially deployed state.

Once the stent 40 and graft 10 are positioned as desired, the releasewire 55 may be pulled to release the secondary stage belt 53 from thebelt retaining structure 50, thereby allowing the stent 40 to fullydeploy as illustrated in FIG. 6. Upon full deployment, the struts 41 arefree to fully radially expand such that the barbs 43 engage the vesselwall 20 in a normal manner.

In addition to facilitating manual movement and repositioning of thegraft 10 and stent 40, the staged deployment of the stent 40 alsofacilitates self-alignment of the stent 40 and graft 10. As explainedabove, upon release of the initial stage belts 35, the graft 10 is freeto expand and distal fluid flow flows into the graft 10 and creates a“windsock” effect. That is, the distal fluid flow expands the graft 10and applies a slight distal force upon the graft 10. This distal forcehelps to align the graft 10 and the stent 40 within the vessel.

This self alignment is particularly advantageous during deployment of astent graft within an angulated vessel, for example, in the aortic arch.Referring to FIG. 7, the stent 40 is illustrated partially deployed inan aortic arch 25. The delivery guidewire chassis 12 contacts the vesselwall 20 and does not remain coaxial with respect to the arch 25. Assuch, in the initial delivery position, the stent 40 may be cocked orotherwise misaligned with respect to the vessel wall 20. In a prior artsingle stage deployment, the stent would expand and the barbs wouldengage the vessel wall even if the stent was misaligned. With the stent40 of the present invention, the initial stage belt(s) 35 are releasedand the stent 40 is partially deployed. The distal fluid flow flows intothe graft 10 and creates the windsock effect, thereby pulling the graft10 and stent 40 into alignment with the flow and thereby the vessel wall20.

Referring to FIGS. 8-13, a pivot fitting 100 configured to assist in themulti-staged deployment of stent 40 will be described. The pivot fitting100 has a generally cylindrical body 102 with an axial through bore 104configured to position the fitting 100 about the guidewire chassis 12(see FIG. 13) or the like. A transverse bore 106 is provided tofacilitate positioning and attachment of the pivot fitting 100 about theguidewire chassis 12 and loading into the delivery catheter (not shown).

The pivot fitting 100 includes an area 108 of reduced cross sectionextending between a shoulder 110 and a radial belt support member 112.The area 108 is configured to receive the free ends of the stent 40, forexample, the mushroom shaped connectors 52 or the crowns 47 with throughholes 54. To facilitate passage of the stent members, the radial beltsupport member 112 includes a plurality of radial slots 114. In theembodiment illustrated in FIG. 13, each radial slot 114 receives thenarrow neck portion of a respective mushroom shaped connector 52.

A circumferential groove 116 is provided along the radial surface of theradial belt support member 112. The circumferential groove 116 isconfigured to receive and maintain the secondary stage belt 53. A beltradial slot 118 is provided in the radial belt support member 112 tofacilitate passage of the secondary stage belt 53 from the guidewirechassis 12 or the like outward to the circumferential groove 116.

Referring to FIG. 11, in the delivery stage, the stent 40 is compactedwith the free end 42 passing through the radial slots 114 in the radialbelt support member 112. The secondary stage belt 53 is secured in thecircumferential groove 116 and constrains the stent free end 42. Turningto FIGS. 12 and 13, upon release of the initial stage release belts 35,the connection end 44 of the stent 40 expands while the free end 42 isretained by the secondary stage belt 53. The opening diameter of theconnection end 44 can be controlled by the relation of the outerdiameter of area 108 and the inner diameter of the circumferentialgroove 116 and the length of the portion of the stent free end 42 thatextends into area 108. In this partially deployed state, the stent freeend 42 is securely retained by the pivot fitting 100, which in turn isconnected to the guidewire chassis 12. As such, movement of theguidewire chassis 12 provides relatively precise control of the positionof the stent 40. Once the stent 40 is positioned in a desired position,the secondary stage belt 53 is released and the stent free end 42disengages from the pivot fitting 100 and expands. The pivot fitting 100remains connected to the guidewire chassis 12 and is removed uponremoval thereof.

While preferred embodiments of the invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes andsubstitutions will occur to those skilled in the art without departingfrom the spirit of the invention. Accordingly, it is intended that theappended claims cover all such variations as fall within the spirit andscope of the invention.

1. A stent-graft system comprising: a graft member; a stent having aconnection end interconnected with the graft member and a free endopposed thereto; a belt retaining structure provided at the stent freeend; and a belt releasably engaging the belt retaining structure andconfigured to constrain the stent free end substantially independent ofthe stent connection end.
 2. The stent-graft system according to claim 1wherein the stent comprises a plurality of struts extending between theconnection end and the free end.
 3. The stent-graft system according toclaim 2 wherein crowns adjoin respective adjacent struts at the free endof the stent.
 4. The stent-graft system according to claim 3 wherein thebelt retaining structure includes a plurality of through holes extendingthrough the crowns.
 5. The stent-graft system according to claim 4wherein the belt is threaded through a plurality of the through holes.6. The stent-graft system according to claim 3 wherein the beltretaining structure includes at least two mushroom shaped connectorsextending from respective crowns.
 7. The stent-graft system according toclaim 2 wherein one or more barbs extend from the stent struts.
 8. Thestent-graft system according to claim 7 wherein the barbs are positionedcloser to the stent free end than the stent connection end.
 9. Thestent-graft system according to claim 1 wherein the belt is releasablysecured by a release wire.
 10. The stent-graft system according to claim1 wherein at least one additional belt is releasably secured about thestent between the connection end and the free end and is releasableindependent from the belt.
 11. The stent-graft system according to claim1 wherein the stent connection end includes a plurality of connectionelements configured for attachment to corresponding connection memberson the tubular graft.
 12. A method of securing at least one end of astent-graft within a vessel, comprising: positioning within the vessel astent-graft comprising a stent and a graft with a connection end of thestent connected to an end of the graft, the stent having a free endopposite the connection end, the stent free end including a beltretaining structure with a belt releasably retained thereabout;deploying the stent connection end within the vessel; repositioning thestent-graft within the vessel, if needed; and releasing the belt todeploy the free end of the stent.
 13. The method according to claim 12wherein the vessel is a thoracic aorta.
 14. The method according toclaim 12 wherein the vessel is an abdominal aorta.
 15. The methodaccording to claim 12 wherein the step of repositioning the stent-graftwithin the vessel includes moving the stent, the graft or a combinationof the stent and the graft.
 16. The method according to claim 12 whereinthe step of repositioning the stent-graft within the vessel includesallowing a fluid flow through the vessel to enter within the graft toself-align the stent and graft.
 17. The method according to claim 12wherein the step of deploying the stent connection end within the vesselincludes releasing an additional belt constraining the stent connectionend.